Solar Thermal Energy

The 233 petawatts of sunlight reaching the Earth’s surface are plentiful compared to the 24 terawatts of average power consumed by humans each year. Within 7 hours, the world’s deserts receive more energy from the sun than humankind consumes within a year. (Dr. Gerhard Knies). Additionally, solar electricity generation has the highest power density among renewable energies, at a global mean of 281 W/m sq. Iraq’s deserts alone generate a power density of 270-290 W/m sq, reaching a peak power density of 2,310 kwh/m sq/year in Iraq’s Western desert, according to NASA.

Solar Thermal Technology’s Suitability for Iraq

All types of concentrated solar power (CSP) plants, using solar thermal technology, are suitable for Iraq. In our review of this topic, we will concentrate on five forms of solar thermal technology and their applications in Iraq: parabolic trough design, solar thermal power towers, Dish Stirling systems, solar updraft towers, and photovoltaic (PV) technology..

1. Parabolic Trough Designs

Parabolic trough power plants are the most successful and cost effective CSP systems at present. They use a curved mirrored trough which reflects the direct sunlight onto a hollow tube running the length of the trough at its focal point. The whole trough tilts through the course of the day so that direct sunlight remains focused on the hollow tube for as long as the sun shines. A fluid, normally thermal oil, passes through the tube and becomes hot. Full-scale parabolic trough systems consist of many such troughs laid out in parallel over a large area of land. A solar thermal system, called the SEGS System, using this principle, is in operation in California in the United States. Operating at 350 MW, SEGS uses oil to absorb the heat generated by

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the sunlight. The oil then passes through a heat exchanger, creating steam, which in turn runs a steam turbine.

2. Solar Thermal Power Tower

r power tower consists of a long field of sun-tracking mirrors, called heliostats, which focus solar energy on a receiver located atop a tall central tower. The sun’s rays are reflected off of the heliostats and concentrated on one point on the tower’s receiver. This enormous amount of energy produces temperatures of approximately 550 degrees Celsius to 1500 degrees Celsius. The gained thermal energy can be used for heating molten salt, which stores the energy for later use. This stored energy is used to heat water and turn it to steam. The steam is then used to move turbines to generate electricity. Through this process, thermal energy is converted into electricity. This technology can produce up to 200 MW depending on the capacity of the hot storage tank and the amount of molten salt used. Examples of solar thermal power towers can be found in Arizona, USA..

3. Dish Stirling System

Dish Stirling systems use a mirror array formed into the shape of a dish to focus the sun’s rays onto a receiver that is mounted on each individual dish. The receiver transmits the energy to a generator, typically a Stirling engine. Solar dish/engine systems convert the sun into electricity at very high net solar-to-electric conversion efficiencies, which can reach up to 30%. This is significantly higher than any other solar technology. A dish Stirling system can operate as stand-alone units in remote locations or can be linked together in groups to provide utility-scale power. Because of the high concentration ratios achievable with parabolic dishes and the small size of the receiver, solar dishes are efficient at collecting solar energy at very high temperatures. Each unit can produce 25KW of energy.

4.Solar Updraft Tower As Developed by the Australian Company Enviromission

In this iteration of solar tower power, the sun's radiation is used to heat a large body of air inside a green¬house like structure around the base of a chimney-like tower. Following the laws of physics, (the adage that “hot air rises”) the heated air moves as a hot wind through large turbines at the tower’s base, generating electricity.

5.Photovoltaic (PV) Technology

Photovoltaic (PV) modules or panels, also known as solar panels, have already proven successful in Iraq. Iraq produces hundreds of megawatts of electricity via PV technology for use in private homes, schools, universities, hospitals, and in the low range of 5KW — 50KW for street lamps. In fact, most street lighting in Baghdad and other Iraqi cities is supplied via PV solar power and many hospitals now have reliable sources of electricity thanks to this technology. Beyond this, Iraq uses PV systems to power water treatment and purification systems. PV technology is the ideal solution for the production of electricity in remote locations though out Iraq. An example of its potential is the 10 MW PV solar power plants in Masdar city, Abu Dhabi.